Israel recently announced the near-completion of a security fence along its southern border with Egypt. Photograph: Getty Images

Israel is to build a huge steel fence along the boundary between the Golan Heights and Syria amid fears that the civil war could spill over or create an influx of refugees.

The pledge from the prime minister, Binyamin Netanyahu, came a few days after the defence ministry announced the near-completion of a 150-mile fence along the southern border with Egypt, aimed mainly at keeping out illegal migrants.

"We intend to erect an identical fence, with a few changes based on the actual territory, along the Golan Heights. We know that on other side of our border with Syria today, the Syrian army has moved away, and in its place, global jihad forces have moved in," Netanyahu told his weekly cabinet meeting on Sunday. "We will defend this border against both infiltration and terrorism, just as we are successfully doing on the [southern] border."

Israeli military sources warned in November that opposition forces had taken control of villages and territory near the United Nations-monitored buffer zone between Syria and the Israeli-occupied Golan Heights, and that fighting in the area had intensified. Several shells fired by regime forces have landed on the Golan. Israel has also said it will take military action if necessary to prevent the regime's chemical weapons falling into the hands of either what it terms "global jihadists" in Syria or Hezbollah in Lebanon.

The Syrian regime was "very unstable", said Netanyahu. "The question of chemical weapons here worries us and … we are coordinating our intelligence and readiness with the United States and others so that we might be prepared for any scenario and possibility that could arise."

Netanyahu's office has declined to comment on recent reports that the prime minister had made a secret visit to King Abdullah of Jordan to discuss the risk of chemical weapons being obtained by Islamic militants.

Israel occupied and later annexed the Golan Heights in 1967, a move not recognised by the international community. Although Israel and Syria are still technically at war, the Golan Heights has been largely quiet in recent decades.

About six miles of the 45-mile boundary has been reinforced in the past 18 months.